Morphologically abnormal sclerotia ofSclerotinia sclerotiorumwere found in samples collected from diseased sunflower head and stem tissues. The frequency of abnormal sclerotia in 22 samples varied from 0 to 30%. Whereas the surface of normal sclerotia is macroscopically smooth and the medullary tissue is uniformly pale white, the surface of abnormal sclerotia is wrinkled and the center of the medullary tissue is brown or amber. The degree of abnormality varies among sclerotia. Some have a small discolored center surrounded by a thick medullary layer, whereas others have a large discolored center encircled by a thin medulla. Abnormal sclerotia also differ from normal ones in viability on culture media as well as in pathogenicity on sunflowers.